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UNT Controller—Unitary (UNT) Controller
The following information should be taken into consideration for specific
rooftop units:
1. Lennox GCS16 Series Rooftop Units
For Lennox GCS16 series rooftop units, bypass the K25 blower/fan
delay relay (TDR) by disconnecting the K25 coil power wire. Lennox
provides K25 blower control for use with electromechanical
thermostats. The reason for disconnecting this when a UNT provides
the blower control functions is that the K25 causes unnecessary
contactor cycling. This creates additional electrical noise. On some
Lennox models, it may also cause blower fan dropout or cycling that
appears as abnormal operation to the customer. Lennox has authorized
bypassing K25 blower control when you use Johnson Controls UNTs.
2. York® Rooftop Units
UNT120-1 and UNT220-1 controllers, when installed in rooftop units,
may experience nuisance resets. This is evidenced by numerous
unexplained offline conditions with durations of less than one minute.
To alleviate this situation in York rooftop units, bypass or disable the
supply fan relay according to the following procedure:
Note: These modifications apply only to those units described below.
Units built after the dates indicated have already been modified
by York and do not require this change.
The date of manufacture of York rooftop units can be
determined from the second and third digits of the serial
number, as shown in Table 40.
•
On 3 to 6 ton units built before February 17, 1997, the K3
relay must be disabled by disconnecting the wire that connects the
time delay relay contacts to the relay board. This is typically the
234/BLUE wire.
•
On 3 to 6 ton units built between February 17, 1997 and
May 30, 1997, York implemented a different relay interface
board. On this new relay board the K5 relay must be bypassed by
moving the wire currently connected to the G terminal on the
York relay board to the A2 terminal.
•
On 7 to 25 ton units built before February 28, 1997, the K5
relay must be bypassed by moving the wire currently connected to
the G terminal on the York relay board to the A2 terminal.
Considerations
for Specific
Rooftop Units
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